The present invention relates to mechanical face seals and in particular to mechanical face seals in which an elastomeric bellows unit provides secondary sealing between one seal face member and its associated component.
In mechanial face seals for providing a seal between a pair of relatively rotatable components, one seal face member is mounted in fixed axial and rotational relationship and sealed with respect to one component while the other seal face member is mounted in fixed rotational relationship and sealed with respect to the other component, but is movable axially thereof. The axially movable seal face member is biased into engagement with the axially fixed seal face member to provide a seal between the engaging faces thereof.
One method of sealing the axially movable seal face member with respect to its associated component is to use an elastomeric bellows unit, one end of which sealingly engages the seal face member and the other end sealingly engages the associated component. The bellows unit may be compressed and expanded axially in order to accommodate axial movement of the seal face member.
Hitherto with seals of this construction in order to achieve sufficient axial compliance, the axial resilience of the bellows unit is low and separate spring means with associated retaining rings have had to be used to bias the seal face members into sealing engagement, for example as disclosed in GB 593,413 and GB 647,587.
In another form of seal, for example as disclosed in GB 2,019,956A, resilient bushes are used to provide a seal between the axially movable seal face member and associated component, compression of the bush serving to axially load the seal face members into sealing engagement. Such bushes will however provide only low axial compliance and the axial load over the operating range will vary considerably.
EP 0,226,845A discloses an elastomeric bellows seal with no separate spring means. The bellows unit of this seal is formed from unreinforced rubber having end portions which sealingly engage a shaft and seal face member, respectively. A relatively thin unsupported intermediate portion is arranged to buckle when the bellows unit is at its working length in order to apply an axial load urging the seal face member into engagement with a seat. With this bellows unit design, when subjected to a pressure differential, this will act on the bellows unit, either side and across the already highly stressed buckled intermediate portion thereof, further stressing this area so that even at relatively low pressure differentials the bellows unit is excessively stressed and liable to split. As a result bellows seals of this construction are limited to use with low pressure differentials up to of the order of 2 bar.
The present invention provides a mechanical face seal with bellows unit which will provide the secondary seal between the axially movable seal face member and associated component and which also applies an axial load urging the seal face members into sealing engagement and is capable of withstanding pressure differentials of the order of 10 bar.